I know. We have that problem as well, when we are short of leads, and no one will upgrade. Why would you give that up when you are already topped out.
In my hub, we had to junior man leads to fill open slots. (They had to be trained and watched over). The IAM is big on Classification Time. In my instance, before we merged and became unionized, we kept our original Company Time and even if you upgraded to Lead or moved to the Move Team, you kept your seniority and leapfrogged over people. (That is why the Javits decision on our seniority had to happen because the company could not or did not kept accurate records on who upgraded or downgraded.) That is why the sCO people kept their original Company Time as when you went into the "upgraded" classification. And rightfully or unrightfully caused conflict with the sUA people at that time. Now, when the contract was ratified, those who wanted to upgrade had to go to the bottom of the list. IMHO, they should have kept the "top out upgrade" as a sort of incentive for junior people who are ready and have the skill to upgrade. But that was lost in the new contract. If you make a lateral move to either Stores or the Aircraft Move Team, you fall to the bottom of their lists. We also have people with higher Company Time on the ramp (usually they came over from Chelsea - which is considered an upgrade) and have more vacation weeks, and higher Sen /Jun for furlough purposes, but their Classification Time is the first day they hit the ramp. So people will go over the lists, and people's time are different. And of course you have to account for lost seniority due to other circumstances. I only know most of this mess because people ask me questions about this, and who is affected. IMHO, I don't think it will be too bad for our workgroup. I am hoping for the best in all of this.
If you make a move (which I know a bunch of people did) to either the AMT or Facility or GSE, you have to follow the IBT contract which places you to the bottom of their lists. You get to keep your Company time for the purposes of vacation and boarding priority, but I'm not sure about the furlough process since it is not considered a lateral move within your Union. But I'm pretty sure your company time would take account in a furlough situation like we are having now. So I'm not sure about that 25 year man with that amount of Company Time who only has 2 or 3 years on the job in the new classification / work position, will keep his job over a 10 year MX who is above him on the seniority list. All I know the Company Time is very important especially in this situation we are in now.
I don't know how the TWU does things, but this is how the IAM does it.